לֹא-תִקַּח הָאֵם, עַל-הַבָּנִים
לֹא-תְבַשֵּׁל גְּדִי, בַּחֲלֵב אִמּוֹ
Two different mitzvot in the Torah, that upon a simple reading would seem to be similar. They're both about the mother/offspring relationship in the animal kingdom, and about compassion or respect for that relationship.
Yet the former is a limited circumstance mitzvah, limited by the chachamim even further to precise conditions. But the latter controls half our lives as observant Jews.
Imagine if Shiluach HaKen was treated like meat & milk? Imagine if we derived a vast body of laws from it the way we do with those 5 simple words about a kid and mother's milk?
We probably wouldn't be allowed to eat eggs and chicken together. And we'd have separate sets of dishes for egg products and fowl products. Or something along those lines.
Why are they so different? I know the traditional answer is that Torah SheBa'al Peh was given at Sinai, and that's the interpretation that was given at that time.
I've been thinking that there might have been an existing tradition of separating meat & milk before the Torah was (re)reveled in Ezra's time, and those laws got shoehorned into a simple line about a baby goat and its mother, so as to provide a divine rationale for the practice. But there weren't any elaborate laws that could tie into Shiluach HaKen, so the original interpretation remained.
After all, the gemara is full of such source seeking - it enlessly asks "minalan"? - where do we know this from? What's the source in Torah SheBichtav? And invariably, the answer is: because pasuk x says something that might parsed in an obscure manner to provide our source. That was likely a part of our tradition well before the Mishna and the Gemara.
So what came first? The chicken or the egg? Just some food for thought.